An atom consists of three fundamental particles: electrons, protons and neutrons. The electrons have negative charge; protons have positive charge while the neutrons have no charge. Structurally, an atom is divided into two parts: nucleus and extra nuclear portion. The nucleus is a tiny, heavy sphere which is present at the centre of an atom. The nucleus of an atom consists of protons and neutrons. Nucleus is positively charged due to the presence of protons in it. The diameter of nucleus ranges from 10–5 to 10–4 m.
The extra nuclear portion consists of negatively charged electrons which revolves around the positively charged nucleus in circular paths called orbits. In an atom, the number of electrons is always equal to that of protons. So, atoms are always electrically neutral.